Explanation:
Saturn's ragged moon Rhea has one of the oldest surfaces known.
Estimated as changing little in the past billion years,
Rhea shows
craters
so old they no longer appear round – their
edges have become compromised by more recent cratering.
Like Earth's Moon,
Rhea's rotation is locked on Saturn, and the
above image shows part of
Rhea's surface that always faces Saturn.
Rhea's leading surface is more highly cratered than its trailing surface.
Rhea is composed mostly of water-ice but is thought to have a
small rocky core.
The above image was taken by the
robot Cassini spacecraft now orbiting Saturn.
Cassini swooped past Rhea two months ago and captured the
above image from about 100,000 kilometers away.
Rhea
spans 1,500 kilometers making it Saturn's second largest moon after
Titan.
Several
surface features on Rhea
remain unexplained including large light patches.